The present invention relates to a magnetic ribbon and a magnetic core formed by using said magnetic ribbon.
If a magnetic core is formed by winding or laminating a magnetic ribbon, and if insulation between layers of the ribbon is poor, an eddy current flowing across the ribbon layers occurs and an increase in eddy current losses results in an increase in overall core losses (magnetic losses). This tendency is particularly noticeable in the case of high frequencies. In addition, the frequency characteristics of permeability is poor, and it is impossible to expect any advantageous use at 100 kHz or more.
Accordingly, in order to improve insulation between ribbon layers, an insulating layer formed of a nonmagnetic material is conventionally provided between the ribbon layers, and a uniform insulating film is formed on the ribbon surface as one means thereof, so as to solve the aforementioned problem.
In cases where an amorphous magnetic ribbon is processed as a magnetic ribbon, annealing is usually carried out at 400.degree. C. or thereabouts. However, if such annealing is carried out, because of a difference in the coefficient of linear expansion, i.e., since the coefficient of linear expansion of the insulating film is greater than that of the amorphous ribbon, compressive stress occurs in the ribbon, and magnetic characteristics deteriorate due to the adverse effect of magnetostriction.
In addition, there is another problem in that materials of such insulating films capable of withstanding annealing at 400.degree. C. or thereabouts are limited. Furthermore, if a magnetic core is formed by providing an insulating film, the filling factor (space factor) declines, which disadvantageously causes the magnetic core to become large in size.